Longitudinal plate assembly having an adjustable length

ABSTRACT

An orthopedic device including a longitudinal plate assembly having an adjustable length and two ends. Each of the ends includes a feature that can be used to couple the end to a body structure, such as, for example, a vertebral bone. Preferably, the assembly includes two longitudinal plates that can translate longitudinally with respect to one another through a plurality of positions and be secured with respect to one another at one of the positions, thereby enabling the length of the assembly to be adjusted. Inasmuch as the length of the plate assembly can be adjusted, the surgeon can set the length to the most clinically appropriate length for effective coupling of the plate assembly to the body structure.

CROSS REFERENCE TO RELATED APPLICATION

[0001] The present application is a continuing application of U.S.patent application Ser. No. 10/075,689 filed Feb. 13, 2002 entitled“Longitudinal Plate Assembly Having an Adjustable Length”, which is acontinuing application U.S. patent application Ser. No. 09/789,938entitled “Longitudinal Plate Assembly Having An Adjustable Length”.

FIELD OF THE INVENTION

[0002] The invention relates generally to a spinal implant assembly forholding vertebral bones fixed relative to one another. Moreparticularly, the invention relates to a longitudinal plate assemblyhaving an adjustable length and two ends that each can be coupled to abody structure, such as a vertebral bone, for use in surgical proceduresfor stabilizing the relative motion of, or permanently immobilizing, thebody structures.

BACKGROUND OF THE INVENTION

[0003] The bones and connective tissue of an adult human spinal columnconsists of more than twenty discrete bones coupled sequentially to oneanother by a tri-joint complex which consist of an anterior disc and thetwo posterior facet joints, the anterior discs of adjacent bones beingcushioned by cartilage spacers referred to as intervertebral discs.These more than twenty bones are anatomically categorized as beingmembers of one of four classifications: cervical, thoracic, lumbar, orsacral. The cervical portion of the spine, which comprises the top ofthe spine, up to the base of the skull, includes the first sevenvertebrae. The intermediate twelve bones are the thoracic vertebrae, andconnect to the lower spine comprising the five lumbar vertebrae. Thebase of the spine includes the sacral bones (including the coccyx). Thecomponent bones of the cervical spine are generally smaller than thoseof the thoracic spine, which are in turn smaller than those of thelumbar region. The sacral region connects laterally to the pelvis. Whilethe sacral region is an integral part of the spine, for the purposes offusion surgeries and for this disclosure, the word spine shall referonly to the cervical, thoracic, and lumbar regions.

[0004] Referring now to FIGS. 1 and 2, a typical vertebral body is shownin a top view and a side view. The spinal cord is housed in the centralcanal 10, protected from the posterior side by a shell of bone calledthe lamina 12. The lamina 12 has three large protrusions, two of whichextend laterally from the shell and are referred to as the transverseprocess 14. The third extends back and down from the lamina and iscalled the spinous process 16. The anterior portion of the spinecomprises a set of generally cylindrically shaped bones which arestacked one on top of the other. These portions of the vertebrae arereferred to as the vertebral bodies 20, and are each separated from theother by the intervertebral discs 22. Pedicles 24 are bone bridges whichcouple the anterior vertebral body 20 to the corresponding lamina 12 andposterior elements 14, 16.

[0005] The spinal column of bones is highly complex in that it includesover twenty bones coupled to one another, housing and protectingcritical elements of the nervous system which have innumerableperipheral nerves and circulatory bodies in dose proximity. In spite ofthese complications, the spine is a highly flexible structure, capableof a high degree of curvature and twist in nearly every direction.

[0006] Genetic or developmental irregularities, trauma, chronic stress,tumors, and disease are a few of the causes which can result in spinalpathologies for which permanent immobilization of multiple vertebralbodies may be necessary. A variety of systems have been disclosed in theart which achieve this immobilization by implanting artificialassemblies in or on the spinal column. These assemblies may beclassified as anterior, posterior, or lateral implants. As theclassification suggests, posterior implants are attached to the back ofthe spinal column, generally hooking under the lamina and entering intothe central canal, attaching to the transverse process, or couplingthrough the pedicle bone. Lateral and anterior assemblies are coupled tothe vertebral bodies.

[0007] The region of the back which needs to be immobilized, as well asthe individual variations in anatomy, determine the appropriate surgicalprotocol and implantation assembly. The use of screw plate assembliesfor stabilization and immobilization via lateral or anterior entranceis, however, common.

[0008] Because spinal injuries vary with regard to the number ofvertebral bodies affected, the proximity of the affected vertebralbodies with respect to one another, and the proximity of the unaffectedor stable vertebral bodies with respect to one another, it is necessaryfor the treatment of a given spinal injury to use a plate assemblyhaving a length that can be used effectively to immobilize, with respectto one another, those vertebral bodies that must be so immobilized toachieve clinically desirable results. For example, depending on thespinal injury, it may be necessary to immobilize two adjacent vertebralbodies. Or, for example, it may be necessary to immobilize two vertebralbodies on either side of one or more unstable or damaged vertebralbodies. Potentially, each spinal injury therefore requires a plateassembly having a different length.

[0009] In addition, the vertebral bodies of the spine are not all equalin length or identical in shape. Some are smaller than others, and aretherefore shorter and, for example, have smaller transverse processes,spinous processes, and/or smaller pedicles. Therefore, depending on thelocation of the spinal injury along the spine, it is again necessary toselect a plate assembly having a length that can be used effectively toimmobilize, with respect to one another, those vertebral bodies thatmust be so immobilized to achieve clinically desirable results. Forexample, in the cervical portion of the spine, the immobilization of twoadjacent vertebral bodies will require a plate assembly of a givenlength, while the immobilization of two adjacent vertebral bodies in thelumbar region will typically require a plate assembly that is longer.And, of course, the selection of the plate assembly of appropriatelength must take into account the specific location of the bonestructures to which the a plate assembly will be coupled, as thesespecific locations vary depending on the spinal injury and the damagecaused thereby.

[0010] Further, because the spine is routinely subject to high loadswhich cycle during movement, one of the primary concerns of physiciansperforming spinal implantation surgeries, as well as of the patients inwhom the implants are placed, is the risk of screw pull-out. Screwpull-out occurs when the cylindrical portion of the bone which surroundsthe inserted screw fails. A bone screw which is implanted perpendicularto the plate is particularly weak because the region of the bone whichmust fail for pull-out to occur is only as large as the outer diameterof the screw threads. It has been found that for pull-out to occur for apair of screws which are angled inward, “toe nailed”, or ones whichdiverge within the bone, the amount of bone which must fail increasessubstantially as compared to pairs of screws which are implanted inparallel along the axis that the loading force is applied. It has,therefore, been an object of those in the art to provide a screw plateassembly which permits the screws to be entered into the vertebral bodyat angles other than 90 degrees.

[0011] A great concern, however, with screws being implanted in theanterior portion of the spine, most particularly in the cervical spine,is that there are important internal tissue structures which, because oftheir proximity to the implant, may be damaged by a dislocated screw. Inthe cervical spine, the esophagus is located directly in front of theanterior surface of the vertebral body, and therefore, in potentialcontact with an implanted cervical plate assembly. Breaches of theesophageal wall permit bacterial contamination of the surroundingtissues, including the critical nerves in and around the spinal cord.Such contamination can be fatal. Because screw pull-out represents oneof the largest risks of esophageal perforation, it has been an object ofthose in the art to produce a cervical screw plate assembly having alocking means which couples, not only the plate assembly to the bone,but locks the screw to the plate assembly. In such a design, it isintended that, even if the bone holding the screw fails, the screw willnot separate from the plate assembly.

[0012] In addition to pull-out, however, it has been observed that ifthe screw plate assembly includes screw heads which protrude beyond theexterior surface of the plate assembly, long term wearing of surroundingtissues may occur, leading to the development of abscesses and holes,which, once again, can have grave consequences. With respect to cervicalplate assemblies, which are necessarily thin, on the order of a fewmillimeters, unless the system is designed to specifically accommodatenon-perpendicular screw-in directions, the heads of the screws which aredesirably toe-nailed in are a considerable risk.

[0013] Similar concerns exist in the thoracic and lumbar regions withrespect to anterior and lateral fixation implants as their areproximally located organs as well as a plurality of major blood vesselswhich may be compromised by either catastrophic screw pull-out and/orlong term wearing of non-flush surface protrusions.

[0014] One screw plate design which has been offered to providephysicians and patients with a reduced risk of pull-out or damage toproximal tissues is the Orion™ Anterior Cervical Plate System of SofamorDanek USA, 1800 Pyramid Place, Memphis, Tenn. 38132. The Orion™ systemteaches a plate having two pair of guide holes through which the screwsare inserted to fix the plate to the vertebral body. The plate furtherincludes external annular recessions about each of the guide holes whichare radially non-symmetric in depth. More particularly, the annularrecessions serve as specific angle guides for the screws so that theymay be inserted non-perpendicularly with respect to the overallcurvature of the plate. In addition, the Orion™ plate includes anadditional threaded hole disposed between each of the pairs of guideholes so that a corresponding set screw may be inserted to lock the bonescrews to the plate.

[0015] Although the Orion™ system achieved certain advantages over priorcervical screw plate assemblies, it is not without failures.Specifically, a given plate can accommodate only one screw-in angulationper hole, preferably in accordance with the angle of the annularrecession. This is undesirable, in that physicians often must inspectthe vertebral bodies during the implantation procedure before making thedecision as to which screw-in angle is the ideal. By forcing thephysician to chose from a limited set of angles, it is unavoidable thatphysicians will be forced to implant plates having screws which werepositioned non-ideally. While providing a variety of plates havingdifferent angle guide holes and annular recession orientations ispossible, the complexity and expense of providing a full spectrum ofplates available in the operating room for the surgeon to choose from isundesirable. It is a failure of the system that one plate cannotaccommodate a variety of different screw-in angles.

[0016] It is an additional failure of the system that an extra set screwis required to lock the screw to the plate. Plates for use in thecervical spine are very thin, and if the screw head already rests in anannular recess, and there is to be enough room for the head of the setscrew to rest on top of the head of the bone screw, the thickness of theremaining plate must be reduced even further. The thinner the plate isat the load bearing points—the guide holes—the weaker the plate isoverall.

[0017] It is a further failure of the system that one plate cannotaccommodate a variety of lengths. Specifically, a given plate canaccommodate only one length, preferably the length that is needed forthe specific injury. This is undesirable, in that physicians often mustinspect the vertebral bodies during the implantation procedure beforemaking the decision as to which plate length is the ideal. By forcingthe physician to chose from a limited set of lengths, it is unavoidablethat physicians will be forced to implant plates having a length that isnon-ideal for the application. This problem is compounded by the limitedset of angles discussed above, in that the physician may be forced touse an angle other than the one most clinically appropriate simplybecause the fixed length of the plate, while being the closestclinically appropriate length available, is slightly too long or tooshort to allow the desired angle to be used. While providing a varietyof plates having different lengths is possible, the complexity andexpense of providing a full spectrum of plates available in theoperating room for the surgeon to choose from is undesirable.

[0018] While the preceding discussion has focused on a specific cervicalscrew plate system and its failures, the same failures apply to the artof vertebral immobilizing screw plate systems which are presentlyavailable as well. There are no presently available screw plateassemblies which present a flush surface and provide for means ofpreventing both screw pull-out from the bone and screw backout from theplate, while simultaneously providing for a wide range of angulation forthe bone screws and for a wide range of plate lengths.

[0019] An additional concern for physicians who implant screw plates forspinal fixation is proper alignment for pre-drilling of the holes intowhich the bone screws are driven to hold the plate. As suggested abovewith respect to the angulation of the annular recesses of the Orion™system, the process of forming the holes generally involves placing theplate against the appropriate vertebral bodies and using a guide to holdthe proper angle with respect to the plate and bone as a drill is used.The difficulty in this process involves slippage at the interfacebetween the unsecured plate and the bone. To avoid slippage, the surgeonis generally required to use, simultaneously, a plate holding mechanism,which may be removably affixed to the plate, to maintain the plate inits proper position, a drill guide to set the desired angulation (whichis set by the thread angle of the plate), and the drill itself. It isunderstood that simultaneous manipulation of these three tools by thesurgeon is tedious and difficult.

[0020] Therefore, there is a need for a new and novel cervical,thoracic, and/or lumbar screw plate assembly having a polyaxial couplingof the screw to the plate assembly, whereby a single plate assembly iscompatible with a wide range of screw-in angles and a wide range ofplate assembly lengths. There is also a need for a screw plate assemblyhaving a flush exterior while being fixed to the vertebral bodies whichit immobilizes, having no screw head protrusion despitenon-perpendicular angulation. There is also a need for a spinal implantassembly which is more sturdy and more versatile than previous designs.There is also a need for a screw plate assembly which provides thesurgeon with the greatest freedom to choose the most desirable angle inwhich to direct the bone screw. There is also a need for an orthopedicscrew plate assembly which has a simple and effective locking mechanismfor locking the bone screw to the plate assembly. There is also a needfor an orthopedic screw plate assembly which has a simple and effectivemeans of holding the plate assembly in position for the pre-drilling ofscrew holes.

SUMMARY OF THE INVENTION

[0021] The invention provides an orthopedic device including alongitudinal plate assembly having an adjustable length and two ends.Each of the ends includes a feature that can be used to couple the endto a body structure, such as, for example, a vertebral bone. Preferably,the assembly includes two longitudinal plates that can translatelongitudinally with respect to one another through a plurality ofpositions and be secured with respect to one another at one of thepositions, thereby enabling the length of the assembly to be adjusted.Inasmuch as the length of the plate assembly can be adjusted, thesurgeon can set the length to the most clinically appropriate length foreffective coupling of the plate assembly to the body structure orstructures.

[0022] In an embodiment, the invention provides a plate assemblyincluding a first longitudinal plate having an end defined bylongitudinal prongs; a second longitudinal plate having a longitudinalbore, the longitudinal bore being adapted to receive the prongs forlongitudinal translation therein through a plurality of positions; and alock assembly for locking the prongs within the bore at one of thepositions. Each plate comprises a feature that can be used to couple theplate to a body structure.

[0023] In an aspect, the bore has an inner surface and the lock assemblypresses the prongs against the inner surface. Preferably, the prongs arelaterally adjacent one another and the lock assembly separates theprongs to press them against the inner surface. The lock assembly caninclude a threaded bore and a set screw passing between the prongs andinto the threaded bore. Alternatively, the lock assembly can include acam that when placed in a first position, does not press the prongsagainst the inner surface, allowing the prongs to longitudinallytranslate freely within the bore through the plurality of positions, andwhen placed in a second position (e.g., rotated 90 degrees with respectto the first position), separates the prongs to press them against theinner surface, preventing longitudinal translation of the prongs withinthe bore.

[0024] In another aspect, a lateral curvature is imparted to the plateassembly. The lateral curvature is preferably contoured to the curvedroughly cylindrical surface of the vertebral bodies to which it can besecured.

[0025] In yet another aspect, at least one of the features comprises athrough hole. Preferably, each feature comprises a pair of throughholes. Preferably, there are two threaded holes at each end of the plateassembly extending through the plate assembly, positioned so that theyare aligned in pairs with the vertebral bodies to which the plateassembly is to be attached.

[0026] In this aspect, the assembly can further include a bone screwhaving a shaft that can be inserted into the through hole and into abone. The shaft can be threaded to cooperate with the threading in thethrough holes. The threading and shaft portion of the bone screws may beof a variety of standard designs, or a particular design which may befound more secure than the standard ones. Preferably, the head is notstandard in that it comprises a semi-spherical section.

[0027] In this aspect, the assembly can further include a couplingelement that has a semi-spherical interior volume and that can beinserted into the through hole. The bone screw can have a semi-sphericalhead that can be rotationally freely mounted within the semi-sphericalinterior volume prior to insertion of the coupling element into thethrough hole. The shaft and the coupling element can be inserted intothe through hole and the shaft can be inserted into the bone at aselected angle within a predetermined range of angles, includingnon-perpendicular angles, relative to the respective plate, therebylocking the coupling element and the head to the respective plate at theselected angle as the head and the coupling element are advanced intothe through hole. For example, the first step in a process of implantingsuch an embodiment of the invention is to position the plate assemblyagainst the vertebral bodies and to align the entry points for thescrews. The next step in such a process is to pre-drill holes into thevertebral bones at desired angles, into which the screws will beinserted. With the plate assembly in place, the screws may be screwedinto the drilled holes in the vertebral bodies.

[0028] In this aspect, the head of the bone screw can have a recess towhich a screwdriving tool can be mated for inserting the screw into thethrough hole and into the bone. The recess can be a slot, phillips,star, hexagonal or other shape that is ideally suited for mating to anappropriate screwdriving tool. When the head of the bone screw issemi-spherical for use with a coupling element in the manner describedabove, however, the recess should not alter the semi-spherical shape ofthe head.

[0029] Accordingly, the coupling element can have a top surface recessthrough which the screwdriving tool may be inserted. The top surfacerecess can be aligned with the recess in the head of the bone screw.This allows the bone screw to be inserted into the bone using thescrewdriver. Alternatively, instead of a recess, the coupling elementmay be partially opened so that the screw and the coupling may bemanipulated easily so that the recess in the head of the screw isaccessible. In either variation, once the screw has been fully insertedinto the vertebral bone, at the desired angle, the coupling element, viaits rotationally free mating of the socket to the inserted screw, isrealigned so that it may be locked down into the plate assembly.Screwing down the coupling element provides the locking of the screw tothe plate assembly, whereby the screw can be angled non-perpendicularly(or perpendicularly, if desired) with respect to the plate assembly,while the coupling element is flush with a bottom surface of one of theplates of the plate assembly, without the need for a set screw.

[0030] In this aspect, the interior semi-spherical interior volume ofthe coupling element can be defined by a curved interior surface whichforms a receiving socket into which the semi-spherical head is inserted,whereby the head is rotationally freely mounted in the semi-sphericalinterior volume. The curved interior surface can include slots whichpermit the interior semi-spherical volume to expand to facilitate theinsertion of the semi-spherical head of the bone screw therein. Thethrough hole can be tapered inwardly to cause, upon insertion of thecoupling element into the through hole, the slots to be compressed,which causes the curved interior surface to lock the semi-spherical headof the screw at a definite insertion angle. Therefore, the couplingelement may be crush-locked to the head of the screw by the applicationof a radial force. The tapering has the effect of applying a radialforce to the slotted socket portion of the coupling element. Thiscircumferential reduction has the desirable effect of locking the screwat the insertion angle. In this way, the coupling element serves as anadditional support for keeping the screw in the vertebral bone at theproper angle.

[0031] It is understood that variations in the coupling element (withrespect to its recessed or open top) can be used without departing fromthe scope of the invention so that polyaxial screws may be used withcervical, thoracic, and lumbar plates, despite the considerablevariation in plate thicknesses.

[0032] In still another aspect, at least one of the plates has a bottomsurface and the assembly further includes at least one featureprotruding from the bottom surface for removable and temporary fixationof the plate assembly to the body structure. Preferably, the featurecomprises a spike. The spike can interface with the vertebral bones tohold the plate assembly in position during the pre-drilling step. Forexample, the plate assembly may be held firmly in place by simplypositioning the plate assembly and applying enough pressure to drive thespikes into the vertebral bone. The spikes will hold the plate assemblyin position, thereby freeing the hands of the surgeon to easily andaccurately pre-drill the ideally angled holes. The spikes also providesupplementary gripping and holding strength for the plate assembly, inaddition to the screws, once the plate assembly has been implantedsecurely.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033]FIG. 1 is a top view of a vertebral bone, the stabilization ofwhich an embodiment of the invention is directed.

[0034]FIG. 2 is a side view of sequentially aligned vertebral bones.

[0035]FIG. 3a is a top view of a first plate of an embodiment of theinvention.

[0036]FIG. 3b is a top view of a second plate of an embodiment of theinvention.

[0037]FIG. 3c is an end view of a first plate of an embodiment of theinvention.

[0038]FIG. 3d is an end view of a second plate of an embodiment of theinvention.

[0039]FIG. 4 is a top view of cooperating first and second plates of anembodiment of the invention.

[0040]FIG. 5 is a side view of a bone screw of a plate assembly of anembodiment of the invention.

[0041]FIG. 6 is a side view of a coupling element of a plate assembly ofan embodiment of the invention.

[0042]FIG. 7 is a partial side cross sectional view of an assembledembodiment of the invention.

[0043]FIG. 8 is a perspective view of a plate assembly of anotherembodiment of the invention.

[0044]FIG. 9a 1 is a top view of a first plate of a second embodiment ofthe invention showing prongs closed.

[0045]FIG. 9a 2 is a top view of a first plate of a second embodiment ofthe invention showing prongs open.

[0046]FIG. 9b is a top view of a second plate of a second embodiment ofthe invention.

[0047]FIG. 9c is an end view of a first plate of a second embodiment ofthe invention.

[0048]FIG. 9d is an end view of a second plate of a second embodiment ofthe invention.

[0049]FIG. 10 is a top view of cooperating first and second plates of asecond embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0050] While the invention will be described more fully hereinafter withreference to the accompanying drawings, in which particular embodimentsand methods of fabrication are shown, it is to be understood at theoutset that persons skilled in the art may modify the invention hereindescribed while achieving the functions and results of this invention.Accordingly, the descriptions which follow are to be understood asillustrative and exemplary of specific structures, aspects and featureswithin the broad scope of the invention and not as limiting of suchbroad scope. Like numbers refer to similar features of like elementsthroughout.

[0051]FIGS. 3a, 3 b, 3 c, 3 d and 4, illustrate elements of a plateassembly 100 of an embodiment of the invention. FIG. 3a illustrates atop view of a first longitudinal plate 100 a of the plate assembly 100.The first plate 100 a has an end 102 defined by longitudinal prongs 102a, 102 b that are laterally adjacent one another. While two prongs areshown in this embodiment, and are shown as laterally adjacent oneanother, it is understood that a greater number of prongs and/or prongsthat are adjacent one another in other configurations can be usedwithout departing from the scope of the invention.

[0052]FIG. 3b illustrates a top view of a second longitudinal plate 100b of the plate assembly 100. The second plate 100 b has an end 104 thathas a longitudinal bore 104 a that is adapted to receive the prongs 102a, 102 b for longitudinal translation therein through a plurality ofpositions. FIG. 4 illustrates a top view of the plate assembly 100 whenthe prongs 102 a, 102 b of the first plate 100 a are received within thebore 104 a of the second plate 100 b. The prongs 102 a, 102 b can beinserted into the bore 104 a and translated longitudinally thereinthrough one or more of the plurality of positions until the desiredlength of the plate assembly 100 is achieved by stopping the translationat one of the positions, such position establishing the desired relativeposition of the first plate 100 a to the second plate 100 b to achievethe desired length of the plate assembly 100.

[0053] The plates 100 a, 100 b may be constructed of any suitablybiocompatible material which has the structural strength and durabilityto withstand the cyclical loading associated with long term fixation tothe spine. Materials which would be suitable for such applicationsinclude titanium alloys and steels. A specific titanium material whichhas been utilized in implants of the prior art include ASTM F-136titanium alloy (Ti 6AL-4V). This material has enhanced mechanicalproperties including fatigue endurance and tensile strength, as comparedwith pure titanium.

[0054] In order to secure the plates 100 a, 100 b in the selectedposition, the plate assembly 100 further includes a lock assembly forlocking the prongs 102 a, 102 b within the bore 104 a at the selectedposition. Activation of the lock assembly secures the relative positionof the plates 100 a, 100 b so that the desired length of the plateassembly 100 is fixed.

[0055]FIG. 3c illustrates an end view of the first plate 100 a. In thisembodiment, as shown in FIG. 3c, the lock assembly includes a threadedbore 100 d between the prongs 102 a, 102 b and a set screw 100 e passingbetween the prongs 102 a, 102 b and into the threaded bore 100 d.Rotation of the set screw 100 e advances the set screw 100 e into thethreaded bore 100 d, causing the prongs 102 a, 102 b to separate as theset screw 100 e passes between them as it advances. Preferably, a headof the set screw 100 e includes a recess that can be mated with ascrewdriving tool and the screwdriving tool can be used to rotate theset screw 100 e within the threaded bore 100 d to advance the set screw100 e until the prongs 102 a, 102 b separate.

[0056]FIG. 3d illustrates an end view of the second plate 100 b. It canbe seen that the bore 104 a has an inner surface 104 b.

[0057]FIG. 4 illustrates a plan view of the plate assembly 100 when theprongs 102 a, 102 b are received within the bore 104 a. The prongs 102a, 102 b are laterally adjacent one another and the lock assemblyseparates the prongs 102 a, 102 b to press them against the innersurface 104 b as described above. The compression of the prongs 102 a,102 b against the inner surface 104 b secures the position of the plates100 a, 100 b relative to one another, thereby fixing the length of theplate assembly 100.

[0058]FIGS. 9a 1, 9 a 2, 9 b, 9 c, 9 d and 10 will now be discussed asdescribing a second embodiment of the present invention that is similarto the first embodiment shown in FIGS. 3a-d and 4 in all materialrespects (and like elements are accordingly like numbered in FIGS. 9a 1,9 a 2, 9 b, 9 c, 9 d and 10) except that this second embodiment has adifferent lock assembly. The discussion will then continue with respectto other aspects of the present invention, which apply to bothembodiments, except where specifically noted.

[0059]FIG. 9c illustrates an end view of the first plate 100 a of thesecond embodiment, in which the lock assembly includes a cam assemblyhaving a cam 900 that when placed in a first position (e.g., as shown inFIG. 9a 1 which is a plan view of the plate assembly 100 of this secondembodiment), does not press the prongs 102 a, 102 b against the innersurface 104 b, allowing the prongs 102 a, 102 b to longitudinallytranslate freely within the bore 104 a through a plurality of positions,and when placed in a second position (e.g., rotated 90 degrees withrespect to the first position as shown in FIG. 9a 2 which is a plan viewof the plate assembly 100 of this second embodiment), separates theprongs 102 a, 102 b to press them against the inner surface 104 b,preventing longitudinal translation of the prongs 102 a, 102 b withinthe bore 104 a.

[0060] For example, a suitable cam 900 would have an elongatedcross-section at that portion 908 of the cam 900 that engages the prongs102 a, 102 b for separation, such that, e.g., the width of the cam 900at that portion 908 is smaller than the resting distance between theprongs 102 a, 102 b (the distance between the prongs 102 a, 102 b whenthey are not engaged by the cam 900), and the length of the cam 900 atthat portion 908 is greater than the combination of the resting distancebetween the prongs 102 a, 102 b and the resting distances between eachprong 102 a, 102 b and the inner surface 104 b (the distances betweenthe prongs 102 a, 102 b and the inner surface 104 b when the prongs 102a, 102 b are not engaged by the cam 900).

[0061] Also, for example, a suitable cam 900 would have at least onefeature that maintains the cam 900 within the plate assembly 100. Oneexample of a suitable feature comprises flanges 906 that prevent the cam900 from slipping out from between the prongs 102 a, 102 b. Preferably,the flanges 906 have a greater cross-section than the length of theportion 908 of the cam 900, as shown. Another example of a suitablefeature comprises a rotatable mounting 902 of the cam 900 to the secondplate 100 b and such that the cam 900 is located between the prongs 102a, 102 b when the prongs 102 a, 102 b are longitudinally translated inthe bore 104 a. Although it need not be in some embodiments, such a cam900 could be made longitudinally translatable in the bore 104 a, e.g.,on a track, so that it can be slid between the prongs 102 a, 102 b toany desired location therebetween, and so positionable at any desiredprong separation location suitable for the length to which the plateassembly 100 has been adjusted. The mounting to the second plate 100 bwould also serve to maintain the cam 900 within the plate assembly 100,and therefore would not require the cam 900 to have flanges 906 tomaintain it within the plate assembly 100.

[0062] Accordingly, when the cam 900 is in the first position, itpreferably can be slid between the prongs 102 a, 102 b to any desiredlocation therebetween, and so is positionable at any desired prongseparation location suitable for the length to which the plate assembly100 has been adjusted. Once the desired prong separation location hasbeen reached, rotation of the cam 900 engages the portion 908 with theprongs 102 a, 102 b to maintain them against the inner surface 104 b.

[0063] It should be understood that other cam types and other rotatablemountings can be used, and fall within the scope of the presentinvention.

[0064]FIG. 9d illustrates an end view of the second plate 100 b of thissecond embodiment, showing that the bore 104 a has the inner surface 104b.

[0065]FIG. 10 illustrates a plan view of the plate assembly 100 of thissecond embodiment when the prongs 102 a, 102 b are received within thebore 104 a. The prongs 102 a, 102 b are laterally adjacent one anotherand when the cam 900 is in the first position (e.g., as shown in FIG. 9a1), the prongs 102 a, 102 b are not pressed against the inner surface104 b, allowing the prongs 102 a, 102 b to longitudinally translatefreely within the bore 104 a through a plurality of positions. Once adesired position of the prongs 102 a, 102 b is reached, the cam 900 canbe slid between the prongs 102 a, 102 b to the most advantageousposition for engaging the prongs 102 a, 102 b, and can be turned. Theturning can be made possible, e.g., by a rotatable mounting of the cam900 between the prongs 102 a, 102 b (e.g., the dimensions of the cam 900discussed above make it possible to rotate the cam 900 between theprongs 102 a, 102 b, and an engageable feature 904 on the cam 900 thatwhen rotated rotates the cam 900. One example of a suitable engageablefeature 904 is a screwdriver-receiving recess as shown. When the cam 900is turned enough to be placed in the second position (e.g., rotated 90degrees with respect to the first position as shown in FIG. 9a 2), thecam 900 separates the prongs 102 a, 102 b and presses them against theinner surface 104 b, preventing longitudinal translation of the prongs102 a, 102 b within the bore 104 a, effectively locking the prongs 102a, 102 b at the desired position.

[0066] With reference again to FIGS. 3c and 3 d, in order to enable theplate assembly 100 to at least grossly conform to the cylindricalmorphology of the vertebral bodies which it couples, a slight lateralcurvature preferably is imparted to the plate assembly 100. Morespecifically, the first plate 100 a has a convex top surface 108 a and aconcave bottom surface 109 a. Similarly, the second plate 100 b has aconvex top surface 108 b and a concave bottom surface 109 b and the bore104 a has a corresponding curvature so that it can receive the prongs102 a, 102 b of the first plate 100 a.

[0067] In order to secure the plate assembly 100 to the desired bodystructure or structures, each plate 100 a, 100 b includes a feature thatcan be used to couple the plate 100 a, 100 b to a body structure. Inthis embodiment, each feature comprises a pair of through holes.However, it should be understood that in other embodiments, additionalor alternative features may be appropriate, including, for example, oneor more hooks, rings, recesses, clips, and adhesives.

[0068] Accordingly, in this embodiment, with reference again to FIGS.3a, 3 b and 4, a first pair of through holes 110, having internalthreading 111, extend fully through the first plate 100 a, from the topsurface 108 a of the plate 100 a through to the bottom surface 109 a ofthe plate 100 a. A second pair of through holes 112, having internalthreading 113, extend fully through the second plate 100 b, from the topsurface 108 b of the plate 100 b through to the bottom surface 109 b ofthe plate 109 b.

[0069] The embodiment shown further includes elements that can be usedin conjunction with the features of the plates 100 a, 100 b to couplethe plates 100 a, 100 b to the body structure. In this embodiment, theelements include screws and cooperative coupling elements. It should beunderstood that elements or tools other than the ones herein describedcan alternatively or additionally be used with the described orsuggested features of the plates 100 a, 100 b to couple the plates 100a, 100 b to the body structures.

[0070] Accordingly, in this embodiment, with reference also to FIG. 5, ascrew of a type which is ideally suited for coupling the plates 100 a,100 b to vertebral bones is shown in a side view. The screw 120comprises a head portion 122, a neck 124, and a shaft 126. In FIG. 5,the shaft 126 is shown as having a tapered shape with a high pitchthread 128. It shall be understood that a variety of shaft designs areinterchangeable with the present design. The specific choice of shaftfeatures, such as thread pitch, or shaft diameter to thread diameterratio, or overall shaft shape, etc. should be made by the physician withrespect to the conditions of the patient's bone, however, the inventionis compatible with a wide variety of shaft designs.

[0071] The head portion 122 of the screw 120 is semi-spherical and has arecess 130. It is understood that the semi-spherical shape isnecessarily a section of a sphere, greater in extent than a hemisphere,and exhibits an external contour which is equidistant from a centerpoint of the head. In a preferred embodiment, the major cross-section ofthe semi-spherical head 122 (as shown in the two dimensionalillustration of FIG. 5) includes at least 270 degrees of a circle.

[0072] The recess 130 defines a receiving locus for the application of atorque for driving the screw 120 into the bone. The specific shape ofthe recess 122 may be chosen to cooperate with any suitable screwdrivingtool. For example, the recess 130 may comprise a slot for a flat-headedscrewdriver, a crossed recess for a phillips head screwdriver, or mostpreferably, a hexagonally shaped hole for receiving an allen wrench. Itis further preferable that the recess 130 be co-axial with the generalelongate axis of the screw 120, and most particularly with respect tothe shaft 126. Having the axes of the recess 130 and the shaft 126co-linear facilitates step of inserting the screw 120 into the bone.

[0073] The semi-spherical head 122 is connected to the shaft 126 at aneck portion 124. While it is preferable that the diameter of the shaft126 be less than the radius of the semi-spherical head 122, it is alsopreferable that the neck 124 of the screw 120 be narrower than thewidest portion of the shaft 126. This preferable dimension permits thescrew to be inserted at a variety of angles while still permitting acoupling element (as described with respect to FIG. 6) to be screwedinto the appropriate hole 110 or 112 of the plate assembly 100 andremain coupled to the head 122.

[0074] As noted above, this embodiment further includes additionalelements that can be used in conjunction with the features of the plates100 a, 100 b to couple the plates 100 a, 100 b to the body structure orstructures. Accordingly, referring now also to FIG. 6, a couplingelement of the invention is shown in side view, wherein phantom linesshow the interior structure of the element along a diametrical crosssection. The coupling element 132 comprises a cylindrical socket havingan external threading 134. The external threading 134 and the diameterof the exterior of the cylindrical socket is designed to mate withthreading 111 or 113 of the holes 110 or 112 of the plate assembly 100,so that the coupling element 132 may be screwed into the plate assembly100. It is preferable that the uppermost thread 135 be designed tocrush-lock the coupling element 132 into the hole 110 or 112. Oncescrewed into the plate assembly 100, and locked down, the top surface136 of the coupling element 132 and the respective top surface 108 a,108 b of the plate assembly 100 present a flush external surface.

[0075] The top surface 136 of the coupling element 132 which is shown inFIG. 6 further comprises a through hole 138, which extends from the topsurface 136 to an interior semi-spherical volume 140. This through hole138 is designed such that the screwdriving tool which is used to insertthe screw 120 into the body structure may access and rotate the screw120 through the coupling element 132.

[0076] The interior semi-spherical volume 140 is ideally suited forholding the head 122 of the screw 120, and permitting the screw 120 torotate through a range of angles. The coupling element 132 has a bottom142 which has a circular hole (enumerated as 143 on the bottom surfaceof the side view of the coupling element in FIG. 6) which forms thebottom entrance into the interior semi-spherical volume 140. It isunderstood that the head 122 of the screw 120 is held within theinterior semi-spherical volume 140 by the annular rim, or support lip,144 of the bottom 142 of the coupling element 132. This annular supportlip 144 defines the circular opening 143 which has a diameter less thanthe diameter of the semi-spherical head 122 of the screw 120.

[0077] It is therefore preferred that the lower portion of the couplingelement 132 comprise slots 146 so that the physician may insert the head122 into the interior volume 140. These slots 146 permit the lowerportion of the coupling element 132 to expand to accept the insertedhead 122, but is secured from releasing the head 122 once the couplingelement 132 is screwed into the plate assembly 100. In an alternativevariation, the holes 110 a or 112 a (as shown in phantom in FIG. 7) ofthe plate assembly 100 are tapered inward with respect to insertiondirection. In such a variation, the step of screwing the couplingelement 132 into the hole 110 a or 112 a causes the slots 146 to becompressed and, correspondingly, for the bottom entrance 143 and theannular lip 144 to lock the screw head 122 into position.

[0078] In the alternative, it is also possible for the coupling element132 to be formed in a manner whereby the lower portion does not have toinclude an expanding entrance 143. In such a variation, the couplingelement 132 would necessarily be formed of two separate pieces whichwould be joined together about the head 122 of the screw 120. In eitherdesign, however, it is preferred than the top surface 136 of thecoupling element 132 have features, such as holes 148, allowing a secondscrewdriving tool to easily insert the element 132 into the threadedholes 110, 100 a or 112, 112 a of the plate assembly 100.

[0079] Referring now to FIG. 7, a partial side cross sectional view of aplate assembly 100 of the invention is shown. With reference to therelative positions of the screw 120, plate assembly 100, and couplingelement 132, the operative steps of implanting this plate assembly 100and affixing it to, for example, a pair of vertebral bones, begins withpreparing the bones through surgical tissue resection and exposure.

[0080] Next, the prongs 102 a, 102 b of the first longitudinal plate 100a are inserted into the bore 104 a of the second longitudinal plate 100b and translated therein until the desired length of the plate assembly100 is achieved. More specifically, the surgeon determines, afterinspection of the vertebral bones to be secured, how far apart the holes110 of the first longitudinal plate 100 a must be spaced from the holes112 of the second longitudinal plate 100 b in order for the plateassembly 100 to be properly coupled to the vertebral bones to beclinically effective.

[0081] Once the surgeon makes this determination, he secures the plates100 a, 100 b in the selection position by locking the lock assembly.More specifically, with regard to the first embodiment (having the lockassembly shown in FIGS. 3a-d and 4), the surgeon uses a screwdrivingtool to rotate the set screw 100 e within the threaded bore 100 d toadvance the set screw 100 e until the prongs 102 a, 102 b separate andpress against the inner surface 104 b of the bore 104 a. The compressionof the prongs 102 a, 102 b against the inner surface 104 b secures theposition of the plates 100 a, 100 b relative to one another, therebyfixing the length of the plate assembly 100. It should be noted thatpreferably, the surgeon is able to use the screwdriving tool to reverserotate the set screw 100 e within the threaded bore 100 d to retract theset screw 100 e and thereby return the prongs 102 a, 102 b back togetherso that they no longer press against the inner surface 104 b of the bore104 a so that the prongs 102 a, 102 b may again freely translate withinthe bore 104 a. This functionality allows the surgeon to readjust thelength of the plate assembly 100 if the surgeon's first setting of thelength is not correct or is undesirable.

[0082] Use of the second embodiment (having the lock assembly shown inFIGS. 9a 1, 9 a 2, 9 b, 9 c, 9 d and 10) by the surgeon is similar inall material respects to use of the first embodiment as noted above,except that locking of the lock assembly involves use of a screwdrivingtool to rotate the cam 900 between the prongs 102 a, 102 b until theprongs 102 a, 102 b separate and press against the inner surface 104 bof the bore 104 a. The compression of the prongs 102 a, 102 b againstthe inner surface 104 b secures the position of the plates 100 a, 100 brelative to one another, thereby fixing the length of the plate assembly100. It should be noted that preferably, the surgeon is able to use thescrewdriving tool to reverse rotate the cam 900 between the prongs 102a, 102 b to return the prongs 102 a, 102 b back together so that they nolonger press against the inner surface 104 b of the bore 104 a so thatthe prongs 102 a, 102 b may again freely translate within the bore 104a. This functionality allows the surgeon to readjust the length of theplate assembly 100 if the surgeon's first setting of the length is notcorrect or is undesirable.

[0083] Once the desired length of the plate assembly 100 is fixed, theplate assembly 100 is positioned against the bones and pre-drill holesare made at the desired insertion angle for the screw 120. Screw 120 andcoupling element 132 are then placed together so that the head 122 iswithin the interior volume 140, whereby the two elements are able torotate freely with respect to one another, but are nonetheless coupled.

[0084] The recess 130 in the screw 120 and the through hole 138 of thecoupling element 132 are aligned at first, and an appropriatescrewdriving tool is used to insert the screw 120 through the properhole 110 or 112 (110 a or 112 a) and into the pre-drilled hole in thebone. Once the screw 120 has been screwed down to the point that thebottom surface of the coupling element 142 contacts the plate 100 a or100 b, the first threads 134 of the coupling element are mated to thethreading 111 or 113 of the hole 110 or 112 (110 a or 112 a),respectively.

[0085] Complete insertion of the coupling element 132 to the plateassembly 100 preferably locks the element 132 to the plate assembly 100,in addition to locking the screw 120 and plate assembly 100 to the bone.In the variation of the embodiment in which the coupling element 132 hasslots (elements 146 of FIG. 6) and an expanding bottom entrance 143,corresponding holes 110 or 112 (110 a or 112 a) may be tapered; thecomplete insertion of the coupling element 132 into the hole 110 or 112therein having the additional benefit of locking the angle of the screw120.

[0086] Referring now to FIG. 8, a variation of the plate assembly 100 ofthe invention is shown in perspective view. This plate assembly 300comprises a first plate 300 a corresponding to the first plate 100 a ofthe plate assembly 100 and a second plate 300 b corresponding to thesecond plate 100 b of the plate assembly 100. The first plate 300 a hasthrough holes 310 and a bottom surface 309 a and the second plate 300 bhas through holes 312 and a bottom surface 309 b. The plate assembly 300further includes at least one feature protruding from one of the bottomsurfaces 309 a, 309 b for removable and temporary fixation of the plateassembly 300 to a vertebral bone. In this embodiment, the feature is aspike. However, it should be understood that other features canadditionally or alternatively be used to achieve this functionalitywithout departing from the scope of the invention.

[0087] Accordingly, in this embodiment, as shown in FIG. 8, one spikeelement 301 protrudes from each of the bottom surfaces 309 a, 309 b.Preferably, each spike 301 is positioned between the pair of holes 310or 312, on center line A-A. These spikes allow the plate assembly 300 tobe temporarily, and easily removably, fixed to vertebral bones duringthe steps of pre-drilling and insertion of the screws 120 through theholes 310, 312 and into the vertebral bones. This is a desirableoperational advantage, as it frees one hand of the surgeon and/orremoves extra tools from the surgical site.

[0088] It is preferred to have the spikes 301 positioned along thecenter line A-A for plate assemblies 300 which have a radius ofcurvature which is equal to or greater than that of the vertebral bodiessuch as, for example, vertebral bones (i.e., not as curved as the bone).Having the spikes 301 along the center line ensures that the plateassembly 300 can be removably fixed to the bone by simply applying aninsertion force against the plate assembly 300 and driving the spikes301 into the bone. It is understood that for implants wherein the plateassembly 300 has a smaller radius of curvature than the bone, it wouldbe desirable to position the spikes 301 at edges 303 of the plateassembly 300.

[0089] While there has been described and illustrated implantationdevices for stabilizing and immobilizing regions of the spine byaffixing a plate assembly having an adjustable length to the anteriorportion of the vertebral bones, it will be apparent to those skilled inthe art that variations and modifications are possible without deviatingfrom the broad spirit and principle of the invention which shall belimited solely by the scope of the claims appended hereto.

What is claimed is:
 1. A plate assembly, comprising: a firstlongitudinal plate having an end defined by longitudinal prongs; asecond longitudinal plate having a longitudinal bore, the longitudinalbore being adapted to receive the prongs for longitudinal translationtherein through a plurality of positions; and a lock assembly forlocking the prongs within the bore at one of the positions; wherein eachplate comprises a feature that is usable to couple the plate to a bodystructure; and wherein the bore has an inner surface and the lockassembly presses the prongs against the inner surface; and wherein theprongs are laterally adjacent one another and the lock assemblyseparates the prongs to press them against the inner surface; andwherein the lock assembly comprises a multi-positionable cam between theprongs.
 2. The plate assembly of claim 1, wherein the cam is alternatelypositionable in a first position, in which the cam permits the prongs tolongitudinally translate within the bore, and a second position, inwhich the cam maintains the prongs against the inner surface.
 3. Theplate assembly of claim 2, wherein when the cam is in the firstposition, it is longitudinally translatable between the prongs through aplurality of longitudinal translation positions.
 4. The plate assemblyof claim 1, wherein the cam is a rotatable cam.
 5. The plate assembly ofclaim 4, wherein the cam is rotatable into a first position, in whichthe cam permits the prongs to longitudinally translate within the bore,and a second position, in which the cam maintains the prongs against theinner surface.
 6. The plate assembly of claim 5, wherein in the secondposition, the cam is rotated ninety degrees with respect to the firstposition.
 7. The plate assembly of claim 5, wherein when the cam is inthe first position, it is longitudinally translatable between the prongsthrough a plurality of longitudinal translation positions.
 8. The plateassembly of claim 1, wherein the cam has a portion that engages theprongs for separation, the portion having a width smaller than a restingdistance between the prongs and a length greater than the restingdistance between the prongs and resting distances between each prong andthe inner surface, wherein the resting distance between the prongs is adistance between the prongs when the prongs are not engaged by the cam,and each of the resting distances between each prong and the innersurface is a distance between each prong and the inner surface when theprongs are not engaged by the cam.
 9. The plate assembly of claim 8,wherein the cam has flanges that maintain the cam in the plate assembly,each of the flanges having a cross-section greater than the length ofthe portion of the cam.
 10. An orthopedic device comprising alongitudinal plate assembly having an adjustable length and two ends,each of the ends comprising a feature that can be used to couple the endto a body structure; wherein the assembly comprises two longitudinalplates that can translate longitudinally with respect to one anotherthrough a plurality of positions and be secured with respect to oneanother at one of the positions, thereby enabling the length of theassembly to be adjusted; and wherein one of the plates has an enddefined by longitudinal prongs and the other of the plates has alongitudinal bore, the longitudinal bore being adapted to receive theprongs for longitudinal translation therein; and wherein the assemblyfurther comprises a lock assembly for locking the prongs within the boreat one of the positions; and wherein the bore has an inner surface andthe lock assembly presses the prongs against the inner surface; andwherein the prongs are laterally adjacent one another and the lockassembly separates the prongs to press them against the inner surface;and wherein the lock assembly comprises a multi-positionable cam betweenthe prongs.
 11. The plate assembly of claim 10, wherein the cam isalternately positionable in a first position, in which the cam permitsthe prongs to longitudinally translate within the bore, and a secondposition, in which the cam maintains the prongs against the innersurface.
 12. The plate assembly of claim 11, wherein when the cam is inthe first position, it is longitudinally translatable between the prongsthrough a plurality of longitudinal translation positions.
 13. The plateassembly of claim 10, wherein the cam is a rotatable cam.
 14. The plateassembly of claim 13, wherein the cam is rotatable into a firstposition, in which the cam permits the prongs to longitudinallytranslate within the bore, and a second position, in which the cammaintains the prongs against the inner surface.
 15. The plate assemblyof claim 14, wherein in the second position, the cam is rotated ninetydegrees with respect to the first position.
 16. The plate assembly ofclaim 14, wherein when the cam is in the first position, it islongitudinally translatable between the prongs through a plurality oflongitudinal translation positions.
 17. The plate assembly of claim 10,wherein the cam has a portion that engages the prongs for separation,the portion having a width smaller than a resting distance between theprongs and a length greater than the resting distance between the prongsand resting distances between each prong and the inner surface, whereinthe resting distance between the prongs is a distance between the prongswhen the prongs are not engaged by the cam, and each of the restingdistances between each prong and the inner surface is a distance betweeneach prong and the inner surface when the prongs are not engaged by thecam.
 18. The plate assembly of claim 17, wherein the cam has flangesthat maintain the cam in the plate assembly, each of the flanges havinga cross-section greater than the length of the portion of the cam.